Traintraintrainssss Stories

On his way to visit his sick grandmother, Callum encounters a young woman in white while waiting for the train to arrive. While sitting next to her on a bench, the young woman tells him events which revolves around him that he thought at first were rubbish until they started to come true. What's going on and how does she know all about it when the future is untold? How will Callum understand the whole situation?